Things you can do when bored...

THINGS YOU CAN DO WITH ABSOLUTELY NOTHING

Blink wildly and then close your eyes really tight for an interesting light show
(Amusement Potential: 1-5 minutes)
See a variety of blobs, stars and flashes. Try to make out shapes and see if your subconscious is trying to send you a message (perhaps that funny shape is saying, 'send all your money to urban75.com'?)

See how long you can hold a note
(Amusement Potential: 4-20 minutes)
Not that much fun, but it sure passes the time. Play with a friend, or try to beat your own personal best. Inhale deeply and then try and make a noise for as long as you can. Earn extra points for making your partner laugh or ending on an amusing note.

Try to not think about penguins
(Amusement Potential: 1-5 minutes)
This is especially hard, because by trying too much, you remember what you were trying to avoid thinking of. If you try too little, you end up thinking about penguins anyway.

Use your secret mind power
(Amusement Potential: 5-10 minutes)
Pick a passing by and try to use your mind power to command them do something, like drop their bag or knock into someone. The law of averages dictates that sooner or later one of your mind commands will come true, so you can convince yourself that you really have super human powers and waste even more time trying them out.

Pretend you're a robot
(Amusement Potential: 1-3 minutes)
Walk down the street with mechanical movements, adding 'zzzzzt' sounds with each motion. Pretending to have a motor broken in, say, your left hand can add at least 30 seconds more entertainment.

Rate passers by
(Amusement Potential: 10-15 minutes)
Secretly award passers by marks out of ten as you go along, offering (unsaid) expert criticism over their clothing, hairstyle and footwear choices.

Repeat the same word over and over until it loses its meaning
(Amusement Potential: 1-3 minutes)
Pick a random word out of a magazine and say it aloud to yourself until it becomes a meaningless set of noises.

Pinch yourself
(Amusement Potential: 1-3 minutes)
What is pain? Why is it unpleasant? There's nothing physical about it - it's all in your mind. Plus, after pinching yourself for awhile, boredom will seem nice next to being in pain.

Try to swallow your tongue
(Amusement Potential: 1-2 minutes)
There's not much to say about this one. It is possible, but really stupid.

Pretend to be a car
(Amusement Potential: 5-10 minutes)
Make appropriate revving noises in your head as you walk along and add a racing commentary as you pass strangers in the street. Use blinking eyes as indicators for extra authenticity.

Make Star Trek door noises
(Amusement Potential: 1-2 minutes)
Stand by an electric door to a bank or something and make that silly "Scccccccchwop" sound heard whenever people popped on to the bridge to hang with Captain Kirk.

Look at something for awhile, shut eyes, study after image
(Amusement Potential: 2-5 minutes)
Another great time waster. It takes about 30 seconds of staring to create an after image, and the image is then viewable for about the same length of time. Fun to combine this one with pushing on your eyes.

Get yourself as nauseated as possible
(Amusement Potential: 5-10 minutes)
Best achieved by looking straight up and spinning around. Try to be so dizzy you can't even stand up. This is also entertaining due to the "makes boredom seem a lot better" effect (see "Hurt Yourself").

Invent a weird twitch
(Amusement Potential: 5-10 minutes)
Adopt a bizarre twitch (e.g. flicking your head irregularly, twitching with eye or busting out sporadic cough noises) and try it out when you go shopping.

Make a low buzzing noise
(Amusement Potential: 15-30 minutes)
Hours of fun in libraries! Keeping a totally straight face and looking nonchalant, make a low pitch humming/buzzing noise and see who reacts.

THINGS YOU CAN DO WITH VERY LITTLE

See what's in your neighbour's rubbish/trash
(Amusement Potential: 20-30 minutes)
You can learn a lot about people by what they throw out. You might uncover some dark secret about them. Plus, they might be throwing out something with value that still works, like a VCR or some porn mags.

Watch TV, repeat everything said in Italian accent
(Amusement Potential: 5-10 minutes)
Sort of entertaining. Include flamboyant shoulder shrugs for added impact, or go for a Marlon Brando set of grunts.

Send spooky emails
(Amusement Potential: 15-60 minutes)
Look up someone's CV on the web, do some research on them via Google and then send them an email full of personal references claiming to be an ex-work colleague who fell in love with their shoes. Or something.

Make prank phone calls
(Amusement Potential: 20-60 minutes)
Very entertaining, but requires discipline. Remember - vulgarities don't make a call funny, but getting the other person to believe a ridiculous story will. Try seeing if you can get them to make noises to 'test' the line. One to get you started off: Call McDonalds with weird complaints about their food.

Pretend all humans will die except for people in room with you
Amusement Potential: 10-20 minutes)
What would you do if this really happened? Would the group stay together, or would there be factions? Who would join what group? Remember, there would only be power for a few days before the plants ran out of fuel or broke. To travel, you would always have to be near cars to siphon gas out of. Best to do with people you know.

Step off a curb with eyes shut, imagine it's a cliff
(Amusement Potential: 2-5 minutes)
To get any benefit out of this one, you have to have a good imagination. Don't step off immediately, build up to the jump. Study the ravine below. Feel the winds at that altitude. Step off and...AHHHHHH!!!!!

Try and sound Welsh
(Amusement Potential: 1-3 minutes)
The key to sounding Welsh is to make sure that your voice goes up at the end of the sentence, so that everything sounds like a question. Throw in a superfluous 'isn't it?' at the end of everything you say and you're halfway there. Isn't it?

Burn things with a magnifying glass
(Amusement Potential: 5-30 minutes)
Ants are always fun to use for this, but burning the face of someone you don't like, under some circumstances, can be just as entertaining.

THINGS YOU CAN DO WITH ANOTHER PERSON

Have a water gargling contest
(Amusement Potential: 5-10 minutes)
Put a glassful of water in your mouth and see how long you can keep gargling for. Award yourself extra points for loud and amusing gargling noises, and minus points if you laugh.

Stare at the back of someone's head until they turn around
(Amusement Potential: 2-5 minutes)
This works on the "I have the feeling I'm being watched" principle. Conduct an experiment-does this really work?

Have a "Who is less competitive" competition
(Amusement Potential: 1-3 minutes)
Trying to win at this will make you lose. Trying to lose makes you win which makes you lose. Not trying at all makes you lose which makes you win which makes you lose.

Pick up a dog so it can see things from your point of view
(Amusement Potential: 3-5 minutes)
Think about it: your dog has only seen the house from a viewpoint from 6" to 2' high (15 to 60 cm for all you metric fans). It's never seen the tops of counters, what you keep on your desk, the tops of shelves, etc. Try looking at things from its point of view, too.

Pull out a hair, stick in someone's ear
(Amusement Potential: 1-5 minutes)
Best done to sleeping people. Added challenge in having no one else around, because then you can't blame it on anyone else. Try to beat your record number of times before the person catches on.

Pour water in hand, make sneeze noise, throw water on back of person's neck
(Amusement Potential: 5-15 minutes)
Always a good gag. For an even bigger reaction out of the person, act like you're not sorry at all for what they think you did. Comment instead on how big that sneeze was or about how there was a lot of mucus in that one.